Analog control provides very fine resolution for output voltage adjustments for switched power supplies. In principle, a voltage can be adjusted to any arbitrary value limited by loop gain, thermal effects and system noise level. On the other hand, a digital control loop has a finite set of discrete “set points” resulting from the resolution of quantizing elements in the system. In a digital control loop of a power supply, two such elements comprise an analog to digital converter and a digital pulse width modulator. Resolution is defined as the number of states that can be uniquely represented by the control word involved. An “n” bit control word can assume 2n states since each bit has two values.
When a power switching stage is modulated by a pulse stream containing 2n possible pulse widths, after averaging by the filter stage, the number of discrete output values equals 2n. Output voltage resolution corresponds to the space between voltage levels. One or more discrete output voltage levels must correspond to the desired output voltage “set point” of the power module including a tolerance. If the resolution in a downstream quantizing element is less than the resolution in the upstream quantizing element, the upstream quantizing element will be unable to find an output voltage that lies within a specific value level for the downstream quantizing element. Thus, one upstream quantizing element LSB change will cause a downstream element to move the output voltage by more than one LSB equivalent. As a result, the system will appear to hunt for a stable value and will bounce up and down around the desired value. This phenomena is called limit cycle oscillation. The limit cycle oscillations occur in a periodic manner which would create an additional tone in the output of the switched power supply. This is undesirable to power supply designs. Thus, there is a need for providing an individual with means for controlling limit cycle oscillations, and in the event limit cycle oscillations are occurring some means for limiting the effects of the periodic nature of the limit cycle oscillations.